The present invention relates to a capacitor and a method for fabricating the same, and a semiconductor device including the capacitor.
Conventionally, capacitors have been formed in a semiconductor device, such as memory devices, DRAM, FRAM, etc., RF devices, analogue devices or logic devices, etc.
The capacitors comprise lower electrodes, a capacitor dielectric film formed on the lower electrodes, and upper electrodes formed on the capacitor dielectric film.
Capacitors using as materials of the lower electrodes and the upper electrodes semiconductors, such as polysilicon, amorphous silicon, etc. are called capacitors of SIS (Silicon Insulator Silicon) structure.
Capacitors using semiconductors as materials of the lower electrodes and metals as materials of the upper electrodes are called capacitors of SIM (Silicon Insulator Metal) structure.
The capacitors of SIS structure and the capacitors of MIS structure use semiconductors, such as polysilicon, etc. in at least the lower electrodes, and the electric resistance of the electrodes are relatively high. The capacitors cannot have good high-speed response.
Then, recently capacitors of MIM (Metal Insulation Metal) structure using metals as materials of the lower electrodes and the upper electrodes are proposed. The capacitors of MIM structure use metals both in the lower and the upper electrodes, and accordingly, the lower electrodes and the upper electrodes have low electric resistances. The capacitors can have good high-speed response.
To form capacitors having good electric characteristics, after the lower electrodes and the capacitor dielectric films have been formed, heat processing of a temperature of above 650xc2x0 C. at lowest must be performed for improving film quality of the capacitor dielectric films. Improved film quality of the capacitor dielectric film is very important to improve voltage resistance of the capacitors and decrease leak current. As metals which can bear the high-temperature heat processing are considered W (tungsten), WN, TiN, Ru, RuO, etc. These materials have relatively high resistivities. Specifically, the resistivity of W is about 6-9 xcexcxcexa9xc2x7cm, the resistivity of WN is about 50 xcexcxcexa9xc2x7cm, the resistivity of TiN is about 50 xcexcxcexa9xc2x7cm, the resistivity of Ru is about 10-15 xcexcxcexa9xc2x7cm, and the resistivity of RuO is about 140 xcexcxcexa9xc2x7cm. On the other hand, Al, which has a low resistivity of 2.7 xcexcxcexa9xc2x7cm but has a low melting point of 630xc2x0 C., cannot unusably withstand the high-temperature heat processing described above. Accordingly, it has been conventionally impossible to form the capacitors of good high-speed response by using materials of low resistivities, such as Al, as materials of the lower electrodes.
When the heat processing for improving film quality of the capacitor dielectric film is performed after the lower electrodes and the capacitor dielectric film which are formed of metals, there is a risk that the lower electrodes will deprive oxygen from the capacitor dielectric film to resultantly deteriorate, to the contrary, film quality of the capacitor dielectric film.
The fabrication process of semiconductor devices is divided largely in bulk steps and layer steps. In the bulk steps, heat processing of high temperatures of about 1000xc2x0 C. are performed, and when metal electrodes are formed in a bulk step, there is a risk of metal contamination. Accordingly, the metal electrodes cannot be formed in a bulk steps. Thus, the capacitors using the metal electrodes cannot be formed on a layer to be formed in a bulk step.
An object of the present invention is to provide a capacitor of good high-speed response and a method for fabricating the capacitor, and a semiconductor device including the capacitor.
According to one aspect of the present invention, there is provided a capacitor comprising a lower electrode formed on a substrate, an upper electrode opposed to the lower electrode, and a capacitor dielectric film formed between the lower electrode and the upper electrode, at least one of the lower electrode and the upper electrode being an electrode of a metal substituted layer.
According to another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode on a substrate; forming a capacitor dielectric film on the lower electrode; forming an upper electrode on the capacitor dielectric film; forming an insulation film on the upper electrode; forming an opening in the insulation film down to the lower electrode; forming a metal layer on the insulation film; and substituting a constituent atom of the lower electrode with a metal atom of the metal layer through the opening to thereby form the lower electrode of a metal substituted layer.
According to further another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode on a substrate; forming a capacitor dielectric film on the lower electrode; forming an upper electrode on the capacitor dielectric film; forming an insulation film on the upper electrode; forming in the insulation film a first opening down to the lower electrode and a second opening down to the upper electrode; forming a metal layer on the insulation film; and substituting a constituent atom of the lower electrode with a metal atom of the metal layer through the first opening to thereby form the lower electrode of a metal substituted layer and substituting a constituent atom of the upper electrode with a metal atom of the metal layer through the second opening to thereby form the upper electrode of a metal substituted layer.
According to further another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode on a substrate; forming a capacitor dielectric film on the lower electrode; forming an upper electrode on the capacitor dielectric film; forming an insulation film on the upper electrode; forming an opening in the insulation film down to the upper electrode; forming a metal layer on the insulation film; and substituting a constituent atom of the upper electrode with a metal atom of the metal layer through the opening to form the upper electrode of a metal substituted layer.
According to further another aspect of the present invention, there is provided a semiconductor device comprising a capacitor including a lower electrode formed on a substrate, an upper electrode opposed to the lower electrode, and a capacitor dielectric film formed at least between the lower electrode and the upper electrode; and at least one of the lower electrode and the upper electrode is an electrode of a metal substituted layer.
According to the present invention, the lower electrodes of polysilicon are formed, and then after the high-temperature heat processing for improving film quality of the capacitor dielectric film has been performed, the lower electrodes of polysilicon is substituted with aluminum to form the lower electrodes of aluminum, whereby aluminum, which cannot withstand the heat processing for improving film quality of the capacitor dielectric film can be used as a material of the lower electrodes. Thus, according to the present invention, capacitors having good high-speed response can be formed.
According to the present invention, the lower electrodes and the upper electrodes of polysilicon are formed, and then the polysiliocn is substituted with aluminum to form the lower electrodes and the upper electrodes of aluminum. Thus, according to the present invention, capacitors having metal electrodes can be formed on a layer formed by a bulk step, where high-temperature processing is performed.
According to the present invention, the divided sectional electrodes of polysilicon are substituted with aluminum, whereby a volume of the sectional electrodes each of which is to be substituted through one opening formed in each sectional electrode can be small. Thus, according to the present invention, the lower electrodes can be substituted with aluminum for a short period of time, and the lower electrodes can be substituted with aluminum without failure.
According to the present invention, polysilicon is substituted with aluminum through the openings formed down to both sides of the sectional electrodes of polysilicon, whereby a period of time in which the sectional electrodes of polysilicon are substituted with aluminum can be half.
According to the present invention, the polysilicon layer is partially left not substituted, whereby capacitors having variable electrostatic capacities can be provided.